A rainbow is an artistic circular color spectrum appearing in the sky, predicted by the Bible as a sign from God after the Great Flood. As explained in Genesis 9:13, God told Noah that the rainbow would remind God and Mankind of God's promise never to flood the Earth again: "I am setting My rainbow in the cloud, and it shall serve as a banner of a binding agreement between Me and the earth."
Physicists describe rainbows based on the refraction and multiple reflections of sunlight in droplets of water. Though appearing semicircular from the ground, rainbows are actually circular. Rainbows appear when water droplets are lit by direct sunlight, a condition that rarely occurs during a storm, because the clouds block the sun. Rainbows are frequently seen after a storm, when the falling rain has moved into the distance and the sun is roughly behind the observer when the observer is facing the patch of rain.
My heart leaps up when I behold
A rainbow in the sky:
So was it when my life began;
So is it now I am a man;
So be it when I shall grow old,
Or let me die!
The Child is father of the Man;
I could wish my days to be
Bound each to each by natural piety.
Complete circular rainbows can be seen under the right conditions; in particular, when viewing the mists over Niagara Falls early or late in the day. Circular rainbows can sometimes be seen from an airplane when it flies over clouds, the rainbow actually encircling the airplane's shadow on the clouds. One way to think about the rainbow is that the mist or rain is like a projection screen, and the rainbow can only be seen where the projection screen is. When the projection screen is large enough, you see the entire circular rainbow.
The rainbow is often depicted inaccurately in pictures. For example, it may be depicted as a three-dimensional object, with perspective, real rainbows never have this appearance. Real rainbows show an extremely subtle blending of color. It is hard to pick out separate colors in a rainbow, but of course to the extent that one can, they appear in the "Roy G. Biv" order, red outermost, then orange, yellow, green, and a range of bluish shades which, in a real rainbow, are hard to distinguish and name. (RoyGBiv stands for "Red, Orange, Yellow, Green, Blue, Indigo, Violet".)
It is extremely difficult to reproduce the subtle, faint pastel colors of a rainbow on a printed page, or even in a color photograph, partly because a rainbow contains colors that are not within the range that can be produced by mixing three primaries, and partly because rainbows are faint; printed depictions of them almost invariably have been enhanced to make them look brighter and more intensely colored than they really are.
A rainbow has also been used as a symbol of homosexuality, specifically the display of a "rainbow flag" showing several color bands. It is a prime example of the corrupting influence of homosexuality on language.
The term "rainbow" has also been used by left-wing political pressure groups to refer to their agenda of multiculturalism, specifically the groups led by Jesse Jackson (the "Rainbow Coalition"), and Lenora Fulani (the "Rainbow Lobby").